Aircraft, and in particular passenger aircraft, are equipped with oxygen supply systems, for example in order to supply passengers with air for breathing or with oxygen in the case of a loss of cabin pressure. In some regions of an aircraft the probability of damage occurring is higher. This applies, for example, to a region of an aircraft where in the case of a malfunction it is possible for parts of power plants to penetrate the aircraft, thus damaging lines, in particular oxygen supply lines. In order to be able to ensure the supply to an adequate number of passengers in such a case, for example two supply lines are provided, wherein each can alternately supply oxygen to every second seat row. In this arrangement, for example, one of these main pipelines can be arranged in the ceiling region and a second one in the subfloor region. By way of ascending lines it is possible, for example, in each case to connect three or four seat rows alternately to the upper or to the lower line. If one of the lines incurs damage, said line can be closed off by way of corresponding valves so as to prevent loss of the entire quantity of oxygen and thus of the entire system. In this case it is provided for the passengers that are affected by the failure of the oxygen supply to be supplied as well by way of the respective seat row in front of or behind the affected seat row, because these seat rows are supplied with oxygen by way of another main pipeline. However, this results in passengers either having to use an oxygen mask alternately in a shared arrangement, or for a corresponding additional number of oxygen masks having to be provided in each row. Furthermore, in such a case of malfunction a relatively long section of the main pipeline has to be closed so that a relatively large number of seats can no longer be supplied.
U.S. Pat. No. 4,651,728 describes a breathing system for high altitude aircraft in which a breathing mask is connected to a pressure controller. The pressure controller is connected to a selector valve, which in turn is connected to an oxygen generating system and to a standby oxygen supply. The selector valve selects the breathing gas from one of these two sources. The oxygen supply system or breathing system described in U.S. Pat. No. 4,651,728 is designed for supplying breathing gas to a pilot.